The high-definition multimedia interface (HDMI) is a compact audio/video connector interface for transmitting uncompressed digital streams. The HDMI connects a digital multimedia (or audio/video) source (e.g., a set-top box, a DVD player, a personal computer, a video game console, etc.) to a compatible digital sink, such as a digital television.
A HDMI cable is a transport medium including three transition minimized differential signaling (TMDS®) channels utilized to transfer video, audio, and auxiliary data encapsulated in TDMS characters, and the transmission is synchronized using a high-frequency clock signal running over a clock channel. The TDMS and clock channels are differential pairs. A HDMI cable also includes the following channels: a display data channel (DDC_SCL and DDC_SDA), a consumer electronics control (CEC), and a hot-plug detect (HPD) signal which originates at the sink.
Recently, the HDMI standard has been enhanced to include an addition of a high-speed full-duplex data communication link (referred to as a HDMI Ethernet Channel (HEC)) that conforms to the 100Base-TX defined in the IEEE 802.3 standard. In the HEC mode, a source and sink device exchange 100Base-TX data through a differential pair, i.e., a single pair of wires is used to transmit and receive simultaneously. In addition, signals (e.g., data frames) are transmitted with attenuated amplitude, compared to the normal 100Base-TX Ethernet signals, on a set of biased lines. The utility and HPD wires in a HDMI cable have been defined to be the differential pair for the HEC communication. The HEC specification is fully described in the HDMI Specification version 1.4, Supplement 2, (hereinafter the “HDMI Standard” published on Jun. 5, 2009, incorporated herein by reference merely for the useful understanding of the background of the invention.
Although designed to support 100Base-TX communication, the HEC is not fully compliant with the Ethernet standard (IEEE 802.3). Specifically, the physical (PHY) layer of the HEC is purposely designed to be different than the PHY layer defined in the IEEE 802.3 standard. Typically, a PHY layer of a communication standard consists of the basic hardware transmission technologies of a network. The most common form of a physical medium used for Ethernet transmission is a twisted pair cable and 8P8C modular connectors also known as RJ45 connectors.
A prime example for the difference between the PHY physical layers of HEC and Ethernet is that HEC is operable only in HDMI devices utilizing connection by means of HDMI cables, thus a standard RJ45 connector is not compatible with the HEC specification. Furthermore, the Ethernet standard defines a half-duplex communication between two devices, where one differential pair is utilized for reception and another differential pair is for transmission. Also, as noted earlier, the HEC signals are attenuated compared to the normal 100Base-TX Ethernet signals.
The fact that the HEC is not fully compliant with the Ethernet standard, limits HDMI devices from being connected to standard network devices, such as routers, hubs, switches, and so on. As a result, an HDMI device cannot support both 100Base-TX Ethernet and HEC. That is, a standard HEC physical layer module cannot drive both HEC and Ethernet connections. This is a limiting factor as a user cannot select a desirable mode of communication for the HDMI device.
The HDMI Standard suggests providing a switch that includes PHY layer modules of both HEC and Ethernet. That is, a PHY layer module of an HEC and a PHY layer of an Ethernet are both fabricated on a chip to support both communication modes. However, in this solution each PHY layer module can operate only according to its respective communication mode.
It would be therefore advantageous to provide a single PHY circuit that supports and drives both the Ethernet and HEC communication standards.